The present invention relates generally to gas valves, and more particularly, to a linear gas valve in which the position of a slide block housed therein can be detected.
On Board Inert Gas Generating Systems (OBIGGS) or On Board Oxygen Generating Systems (OBOGS) utilize molecular sieve by employing a pressure swing adsorption (PSA) process that has been used for many years to generate either nitrogen or oxygen product sequentially, respectively. This process of sequential pressurization and venting is the PSA process. This PSA technology uses conditioned engine bleed air fed through the valve to pressurize molecular sieve contained in each of a number of canisters. After a predetermined period of time, a valve changes state, venting the one pressurized canister and then pressurizing the next canister. Previous PSA systems have been controlled by a rotary valve which is controlled by a valve and driven by a fixed or variable speed motor.
Recent PSA systems utilize a linear 4-way slide valve, which connects, input air with one canister, while connecting a vent port with another canister. The valve changes state, which connects the vent port with the first canister and simultaneously connecting the second canister with the input air.
The linear valve used on typical PSA systems is pneumatically operated using control pilot gas from miniature pilot solenoid valves and are opened and closed using solid state electronics which are housed in an EMI shielded enclosure. The pilot solenoids provide gas pressure to two gas cylinders, which are connected to a sliding block. The block slides across a mating plate with three openings or ports. The ports are constructed in a straight line. The outer ports are equal-distance from center port. The sliding block has an undercut, which acts as a flow path. The flow path is sized to connect two of the three ports at any one point in time. A controller is set to open and close the miniature pilot valves at a predetermined time or xe2x80x9ccycle timexe2x80x9d.
The PSA device functions by forcing the undesired gas molecules into xe2x80x9csitesxe2x80x9d in the molecular sieve. The cycle time of the PSA process is largely determined by what purity is desired of the product gas. Using the linear valve, the slide block is controlled to provide the air to the desired canister and simultaneously vent the other canister. If the slide block slows down the resulting purity changes.
Airborne OBOGS systems usually have oxygen monitors to detect oxygen purity degradation and alarm the operator/pilot of a failure to produce desired oxygen. There are a number of internal and external conditions which result in poor oxygen. One internal condition which would cause poor purity would be a slide valve, which did not change state or changed state slower than desired. Airborne OBIGGS systems do not have nitrogen monitors. Some systems use an oxygen monitor and infer the nitrogen purity from the amount of residual oxygen in the product system. Nitrogen product purity is affected in the same manner as oxygen product purity if the slide valve fails to operate properly. External conditions which cause oxygen purity degradation include ambient temperature, below normal operating pressure, sieve degradation, moisture, etc.
The PSA process handles moisture entrained in the air during normal operation. If moisture enters the system through the air system, when the PSA process is not operating, the result is permanent damage to the molecular sieve. Damaged sieve does not separate air. Many OBOGS and OBIGGS systems have separate shut-off valves which prevent the entrance of air into the molecular sieve beds when the system is not operating. Thus, a need exists in the art for a linear valve having a slide block in which the current position of the slide block can be detected. Another need exists for a linear valve in which the separate shut-off valve is eliminated.
It is, therefore, an object of the present invention to provide a linear valve and control system in which the location of the slide block is monitored to trouble shoot performance problems before they occur.
Another object of the present invention is to provide a linear valve having a slide block in which the position is monitored by a sensing device.
Another object of the present invention is to provide a linear valve in which a shutoff valve is eliminated between the linear valve and an air source.
The present invention relates to detecting the state of a slide block positioned in a linear valve and using the position of the slide block to predict the health of a linear valve and provide information to a controller/monitor. An operator is provided with information before failure occurrence to allow preventative maintenance of the linear valve.
The linear valve is constructed with two canister ports and a vent port. The slide block can be constructed to block the two canister ports and vent port simultaneously. The system can control the position of the block, when provided with position information, hence, using the slide block as a shutoff valve. The typical slide valve can be used as an integral slide shutoff valve, reducing system complexity and reducing system weight, which is critical to airborne applications.
These and other objects of the present invention are achieved by a control system for controlling a gas generating system including at least two molecular sieve beds. A linear valve has a housing including an inlet connected to the gas generating system and a first port connected to a first of the at least two molecular sieve beds, a second port for exhaust, and a third port connected to a second of the at least two molecular sieve beds. The inlet, the first, second and third ports are all in communication with a slide chamber in the housing. A slide block is positioned in the slide chamber. A push-pull device is mounted to the housing for moving the slide block in a first direction and in a second direction. A sensor is positioned at opposite ends of the slide chamber for sensing the position of the slide block in the slide chamber. A controller is provided for receiving information from the sensing device and for controlling the push-pull device.
The foregoing and other objects of the present invention are also achieved by a linear valve including a housing. The housing includes an inlet connected to a gas generating system and a first port connected to a first of at least two molecular sieve beds, a second port for exhaust, and a third port connected to a second of the at least two molecular sieve beds, with the inlet, the first, second and third ports all in communication with a slide chamber in the housing with a slide block positioned in the slide chamber. A push-pull device is mounted to the housing for moving the slide block in a first direction and in a second direction. A sensor is positioned at opposite ends of the slide chamber for sensing the position of the slide block in the slide chamber.
The foregoing and other objects of the present invention are also achieved by a method of monitoring an operational status of a linear valve including detecting when a linear slide block is in one of at least two positions, determining at least one of slew rate, full length stroke and uneven stroke and alerting a user if one of the slew rate, full length stroke and uneven stroke exceeds a predetermined value.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.